A comparison of membranes and enrichment strategies for microbial fuel cells

The external resistance is perhaps the easiest way to influence the operation of a microbial fuel cell (MFC). In this paper, three enrichment strategies, whereby the external resistance was fixed at: (1) a high value in order to maximize the cell voltage (U strategy); (2) a low value in order to maximize the current (I strategy); and (3) a value equal to the internal resistance of the MFC to maximize the power output (P strategy), were investigated. The I strategy resulted in increased maximum power generation and the likely reason is that electron transfer was facilitated under low external resistance, which in turn, favored the development of an electrochemically active biofilm. This experiment was conducted in a single-chamber MFC system equipped with a membrane electrode assembly, and a comparison of the performance achieved by five different membranes is also provided. Selemion was found to be a suitable alternative to Nafion.     

High shear enrichment improves the performance of the anodophilic microbial consortium in a microbial fuel cell

In many microbial bioreactors, high shear rates result in strong attachment of microbes and dense biofilms. In this study, high shear rates were applied to enrich an anodophilic microbial consortium in a microbial fuel cell (MFC). Enrichment at a shear rate of about 120 s^?1 resulted in the production of a current and power output two to three times higher than those in the case of low shear rates (around 0.3 s^?1). Biomass and biofilm analyses showed that the anodic biofilm from the MFC enriched under high shear rate conditions, in comparison with that under low shear rate conditions, had a doubled average thickness and the biomass density increased with a factor 5. The microbial community of the former, as analysed by DGGE, was significantly different from that of the latter. The results showed that enrichment by applying high shear rates in an MFC can result in a specific electrochemically active biofilm that is thicker and denser and attaches better, and hence has a better performance.     

Bacterial community structure, compartmentalization and activity in a microbial fuel cell

AIMS: To characterize bacterial populations and their activities within a microbial fuel cell (MFC), using cultivation-independent and cultivation approaches. METHODS AND RESULTS: Electron microscopic observations showed that the fuel cell electrode had a microbial biofilm attached to its surface with loosely associated microbial clumps. Bacterial 16S rRNA gene libraries were constructed and analysed from each of four compartments within the fuel cell: the planktonic community; the membrane biofilm; bacterial clumps (BC) and the anode biofilm. Results showed that the bacterial community structure varied significantly between these compartments. It was observed that Gammaproteobacteria phylotypes were present at higher numbers within libraries from the BC and electrode biofilm compared with other parts of the fuel cell. Community structure of the MFC determined by analyses of bacterial 16S rRNA gene libraries and anaerobic cultivation showed excellent agreement with community profiles from denaturing gradient gel electrophoresis (DGGE) analysis. CONCLUSIONS: Members of the family Enterobacteriaceae, such as Klebsiella sp. and Enterobacter sp. and other Gammaproteobacteria with Fe(III)-reducing and electrochemical activity had a significant potential for energy generation in this system. SIGNIFICANCE AND IMPACT OF THE STUDY: This study has shown that electrochemically active bacteria can be enriched using an electrochemical fuel cell.     

Electricity generation from mixed volatile fatty acids using microbial fuel cells

Fermentative hydrogen production, as a process for clean energy recovery from organic wastewater, is limited by its low hydrogen yield due to incomplete conversion of substrates, with most of the fermentation products being volatile fatty acids (VFAs). Thus, further recovery of the energy from VFAs is expected. In this work, microbial fuel cell (MFC) was applied to recover energy in the form of electricity from mixed VFAs of acetate, propionate, and butyrate. Response surface methodology was adopted to investigate the relative contribution and possible interactions of the three components of VFAs. A stable electricity generation was demonstrated in MFCs after the enrichment of electrochemically active bacteria. Analysis showed that power density was more sensitive to the composition of mixed VFAs than coulombic efficiency. The electricity generation could mainly be attributed to the portion of acetate and propionate. However, the two components showed an antagonistic effect when propionate exceeded 19%, causing a decrease in coulombic efficiency. Butyrate was found to exert a negative impact on both power density and coulombic efficiency. Denaturing gradient gel electrophoresis profiles revealed the enrichment of electrochemically active bacteria from the inoculum sludge. Proteobacteria (Beta-, Delta-) and Bacteroidetes were predominant in all VFA-fed MFCs. Shifts in bacterial community structures were observed when different compositions of VFA mixtures were used as the electron donor. The overall electron recovery efficiency may be increased from 15.7% to 27.4% if fermentative hydrogen production and MFC processes are integrated.     

Modeling the Impact of Interspecies Competition on Performance of a Microbial Fuel Cell

Previous models of biofilms growing in a microbial fuel cell (MFC) have primarily focused on modeling a single growth mechanism: growth via a conductive biofilm matrix, or growth utilizing diffusible electron shuttles or mediators. In this work, we implement both flavors of models in order to explore the competition for space and nutrients in a MFC biofilm populated by both species types. We find that the optimal growth conditions are for bacteria that utilize conductive EPS provided a minimal energy used to create the EPS matrix. Mediator-utilizing bacteria do have favorable niche regions, most notably close to the anode and where exposed to the bulk inflow, where oxidized mediator is readily available.     

Operational temperature regulates anodic biofilm growth and the development of electrogenic activity

The operational temperature of microbial fuel cell reactors influences biofilm development, and this has an impact on anodic biocatalytic activity. In this study, we compared three microbial fuel cell (MFC) reactors acclimated at 10°C, 20°C and 35°C to investigate the effect on biomass development, methanogenesis and electrogenic activity over time. The start-up time was inversely influenced by temperature, but the amount of biomass accumulation increased with increased temperatures, the 10°C, 20°C and 35°C acclimated biofilms resulted in 0.57, 0.82 and 5.43 g biomass (volatile suspended solids) per litre respectively at 56 weeks of operation. Biofilm build-up on the 35°C anode was further demonstrated by scanning electron microscopy, which showed large aggregations of biomass accumulating on the anode when compared to 10°C and 20°C biofilms. Biomass accumulation had a direct impact on biocatalytic performance, with the maximum power at 35°C after 60 weeks of operation being 2.14 W m⁻³ and power densities for the 10°C and 20°C reactors being and 4.29 W m⁻³. Methanogenic activity was also shown to be higher at 35°C, with a rate of 10.1 mmol CH₄ biofilm per gram of volatile suspended solid (VSS) per day, compared to 0.28 mmol CH₄ per gram of VSS per day produced at 20°C. These results demonstrate that higher MFC operating temperatures could be detrimental to the biocatalytic performance of electrochemically active bacteria in anodic biofilms due to biomass accumulation with enhanced development of non-electrogenic communities (e.g. methanogens and fermenters), meaning that, over time, psychro- or mesophilic operation can have beneficial effects for the development of electrogenically active populations in the reactor.     

Microbial fuel cell characterisation and evaluation of <Emphasis Type="Italic">Lysinibacillus macroides</Emphasis> MFC02 electrigenic capability

Microbial fuel cell (MFC) is the most prominent research field due to its capability to generate electricity by utilizing the renewable sources. In the present study, Two MFC designs namely, H type-Microbial fuel cell (HT-MFC) and U type-Microbial fuel cell (UT-MFC) were constructed based on standardized H shaped anode and cathode compartment as well as U shaped anode and cathode compartments, respectively. In order to lower the cost for MFC construction, Pencil graphite lead was used as electrode and salt agar as Proton exchange membrane. Results inferred that newly constructed UT-MFC showed high electron production when compared to the HT-MFC. UT-MFC displayed an output of about 377?±?18.85 mV (millivolts); whereas HT-MFC rendered only 237?±?11.85 mV (millivolts) of power generation, which might be due to the low internal resistance. By increasing the number of cathode in UT-MFC, power production was increased upto 313?±?15.65 mV in Open circuit voltage (OCV). Electrogenic bacteria namely, Lysinibacillus macroides (Acc. No. KX011879) rendered enriched power generation. The attachment of bacteria as a biofilm on pencil graphite lead was analyzed using fluorescent microscope and Scanning Electron Microscope (SEM). Based on our findings, it was observed that UT-MFC has a tendency to produce high electron generation using pencil graphite lead as the electrode material.     

Enhanced reductive degradation of methyl orange in a microbial fuel cell through cathode modification with redox mediators

A model azo dye, methyl orange (MO), was reduced through in situ utilization of the electrons derived from the anaerobic conversion of organics in a microbial fuel cell (MFC). The MO reduction process could be described by a pseudo first-order kinetic model with a rate constant of 1.29 day⁻¹. Electrochemical impedance spectroscopic analysis shows that the cathode had a high polarization resistance, which could decrease the reaction rate and limit the electron transfer. To improve the MO reduction efficiency, the cathode was modified with redox mediators to enhance the electron transfer. After modification with thionine, the polarization resistance significantly decreased by over 50%. As a consequence, the MO decolorization rate increased by over 20%, and the power density was enhanced by over three times. Compared with thionine, anthraquinone-2, 6-disulfonate modified cathode has less positive effect on the MFC performance. These results indicate that the electrode modification with thionine is a useful approach to accelerate the electrochemical reactions. This work provides useful information about the key factors limiting the azo dye reduction in the MFC and how to improve such a process.     

Evaluation of procedures to acclimate a microbial fuel cell for electricity production

A microbial fuel cell (MFC) is a relatively new type of fixed film bioreactor for wastewater treatment, and the most effective methods for inoculation are not well understood. Various techniques to enrich electrochemically active bacteria on an electrode were therefore studied using anaerobic sewage sludge in a two-chambered MFC. With a porous carbon paper anode electrode, 8 mW/m² of power was generated within 50 h with a Coulombic efficiency (CE) of 40%. When an iron oxide-coated electrode was used, the power and the CE reached 30 mW/m² and 80%, respectively. A methanogen inhibitor (2-bromoethanesulfonate) increased the CE to 70%. Bacteria in sludge were enriched by serial transfer using a ferric iron medium, but when this enrichment was used in a MFC the power was lower (2 mW/m²) than that obtained with the original inoculum. By applying biofilm scraped from the anode of a working MFC to a new anode electrode, the maximum power was increased to 40 mW/m². When a second anode was introduced into an operating MFC the acclimation time was not reduced and the total power did not increase. These results suggest that these active inoculating techniques could increase the effectiveness of enrichment, and that start up is most successful when the biofilm is harvested from the anode of an existing MFC and applied to the new anode.     

Use of acetate for enrichment of electrochemically active microorganisms and their 16S rDNA analyses

A fuel cell-type electrochemical device has been used to enrich microbes oxidizing acetate with concomitant electricity generation without using an electron mediator from activated sludge. The device generated a stable current of around 5 mA with complete oxidation of 5 mM acetate at the hydraulic retention time of 2.5 h after 4 weeks of enrichment. Over 70% of electrons available from acetate oxidation was recovered as current. Carbon monoxide or hydrogen did not influence acetate oxidation or current generation from the microbial fuel cell (MFC). Denaturing gradient gel electrophoresis showed that DNA extracted from the acetate-enriched MFC had different 16S rDNA patterns from those of sludge or glucose+glutamate-enriched MFCs. Nearly complete 16S rDNA sequence analyses showed that diverse bacteria were enriched in the MFC fed with acetate. Electron microscopic observations showed biofilm developed on the electrode, but not microbial clumps observed in MFCs fed with complex fuel such as glucose and wastewater from a corn-processing factory.     

A comparison of air and hydrogen peroxide oxygenated microbial fuel cell reactors

In this study, a two-compartment continuous flow microbial fuel cell (MFC) reactor was used to compare the efficiencies of cathode oxygenation by air and by hydrogen peroxide. The MFC reactor had neither a proton-selective membrane nor an electron transfer mediator. At startup, the cathodic compartment was continuously aerated and the anodic compartment was fed with a glucose solution. An increase of electrical power generation from 0.008 to 7.2 mW m(-2) of anode surface with a steady-state potential of 215-225 mV was observed within a period of 12 days. The performance of the air-oxygenated MFC reactor progressively declined over time because of biofilm proliferation in the cathodic compartment. Oxygenation of the cathodic compartment using 300 mL d(-1) of 0.3% hydrogen peroxide solution resulted in a power density of up to 22 mW m(-2) (68.2 mA m(-2)) of anode surface at a potential of 340-350 mV. The use of H2O2 for oxygenation was found to improve the long-term stability of the MFC reactor.     

Development of Enterobacter aerogenes fuel cells: From in situ biohydrogen oxidization to direct electroactive biofilm

This study described an Enterobacter aerogenes-catalyzed microbial fuel cell (MFC) with a carbon-based anode that exhibited a maximum power density of 2.51 W/m³ in the absence of artificial electron mediators. The MFC was started up rapidly, within hours, and the current generation in the early stage was demonstrated to result from in situ oxidation of biohydrogen produced by E. aerogenes during glucose fermentation. Over periodic replacement of substrate, both planktonic biomass in the culture liquid and hydrogen productivity decreased, while increased power density and coulombic efficiency and decreased internal resistance were unexpectedly observed. Using scanning electron microscopy and cyclic voltammetry, it was found that the enhanced MFC performance was associated with the development of electroactive biofilm on the anodic surface, proposed to involve an acclimation and selection process of E. aerogenes cells under electrochemical tension. The significant advantage of rapid start-up and the ability to develop an electroactive biofilm identifies E. aerogenes as a suitable biocatalyst for MFC applications.     

Understanding interactive characteristics of bioelectricity generation and reductive decolorization using Proteus hauseri

This first-attempt study quantitatively explored interactive characteristics of bioelectricity generation and dye decolorization in air-cathode single-chamber microbial fuel cells (MFCs) using indigenous Proteus hauseri ZMd44. After approx. 15 cycles (30 days) acclimatization in dye-bearing cultures, P. hauseri could express its stable capability of simultaneous bioelectricity generation and color removal (SBP&CR) in MFCs. Evidently, appropriate acclimation strategy for formation of the electrochemically active anodic biofilm played a crucial role to enhance the performance of SBP&CR in MFCs. Gradually increased supplementations of C.I. reactive blue 160 resulted in progressively decreased decay rate of bioelectricity generation. That is, a dye decolorized in a faster rate would result in a lower capability for bioelectricity generation and vice versa. In addition, a reduced dye with less toxicity potency (e.g., 2-aminophenol) might work as a redox mediator of electron transport to anodic biofilm for bioelectricity generation in MFCs.     

Performance and microbial diversity of palm oil mill effluent microbial fuel cell

Aim: To evaluate the bioenergy generation and the microbial community structure from palm oil mill effluent using microbial fuel cell. Methods and Results: Microbial fuel cells enriched with palm oil mill effluent (POME) were employed to harvest bioenergy from both artificial wastewater containing acetate and complex POME. The microbial fuel cell (MFC) showed maximum power density of 3004 mW m^?2 after continuous feeding with artificial wastewater containing acetate substrate. Subsequent replacement of the acetate substrate with complex substrate of POME recorded maximum power density of 622 mW m^?2. Based on 16S rDNA analyses, relatively higher abundance of Deltaproteobacteria (88·5%) was detected in the MFCs fed with acetate artificial wastewater as compared to POME. Meanwhile, members of Gammaproteobacteria, Epsilonproteobacteria and Betaproteobacteria codominated the microbial consortium of the MFC fed with POME with 21, 20 and 18·5% abundances, respectively. Conclusions: Enriched electrochemically active bacteria originated from POME demonstrated potential to generate bioenergy from both acetate and complex POME substrates. Further improvements including the development of MFC systems that are able to utilize both fermentative and nonfermentative substrates in POME are needed to maximize the bioenergy generation. Significance and Impact of the Study: A better understanding of microbial structure is critical for bioenergy generation from POME using MFC. Data obtained in this study improve our understanding of microbial community structure in conversion of POME to electricity.     

Enhanced Cathodic Oxygen Reduction and Power Production of Microbial Fuel Cell Based on Noble‐Metal‐Free Electrocatalyst Derived from Metal‐Organic Frameworks

Microbial fuel cell (MFC) can generate electricity from organic substances based on anodic electrochemically active microorganisms and cathodic oxygen reduction reaction (ORR), thus exhibiting promising potential for harvesting electric energy from organic wastewater. The ORR performance is crucial to both power production efficiency and overall cost of MFC. A new type of metal‐organic‐framework‐derived electrocatalysts containing cobalt and nitrogen‐doped carbon (CoNC) is developed, which is effective to enhance activity, selectivity, and stability toward four‐electron ORR in pH‐neutral electrolyte. When glucose is used as the substrate, the maximum power density of 1665 mW m^?2 is achieved for the optimized CoNC pyrolyzed at 900 °C, which is 39.8% higher than that of 1191 mW m^?2 for commercial Pt/C catalyst in the single‐chamber MFC. The improved performance of CoNC catalyst can be attributed to large surface area, microporous nature, and the involvement of nitrogen‐coordinated cobalt species. These properties enable the efficient ORR by increasing the active sites and enhancing mass transfer of oxygen and protons at “water‐flooding” three‐phase boundary where ORR occurs. This work provides a proof‐of‐concept demonstration of a noble‐metal‐free high‐efficiency and cost‐effective ORR electrocatalyst for effective recovery of electricity from biomass materials and organic wastewater in MFC.     

Impact of anodophilic biofilm bioelectroactivity on the denitrification behavior of air-cathode microbial fuel cells

Generally, high bioelectroactivity of anodophilic biofilm favors high power generation of microbial fuel cell (MFC); however, it is not clear whether it can promote denitrification of MFC synchronously. In this study, we studied the impact of anodophilic biofilm bioelectroactivity on the denitrification behavior of air-cathode MFC (AC-MFC) in steady state and found that high bioelectroactivity of anodophilic biofilm not only favored high power generation of the AC-MFC, but also promoted the growth of denitrifers at the anodes and strengthened denitrification. Anodophilic biofilms of AC-MFC with various bioelectroactivity were acclimated at conditions of open circuit (OC), R_ext of 1000 Ω and 20 Ω (denoted as AC-MFC-OC, AC-MFC-1000Ω, and AC-MFC-20Ω, respectively) and performed for over 100 days. Electrochemical tests and microbial analysis results showed that the anode of the AC-MFC-20Ω delivered higher current response of both oxidation and denitrification and had higher abundance of electroactive bacteria than the AC-MFC-OC, AC-MFC-1000Ω, demonstrating a higher bioelectroactivity of the anodophilic biofilms. Moreover, these electroactive bacteria favored the accumulation of denitrifers, like Thauera and Alicycliphilus, probably by consuming trace oxygen through catalyzing oxygen reduction. The AC-MFC-20Ω not only delivered a 61.7% higher power than the AC-MFC-1000Ω, but also achieved a stable and high denitrification rate constant (k_DN) of 1.9 h^?1, which was 50% and 40% higher than that of the AC-MFC-OC and AC-MFC-1000Ω, respectively. It could be concluded that the high bioelectroactivity of the anodophilic biofilms not only favored high power generation of the AC-MFC, but also promoted the enrichment of denitrifers at the anodes and strengthened denitrification. This study provided an effective method for enhancing power generation and denitrification performance of the AC-MFC synchronously.     

奥奈达希瓦氏菌电活性生物被膜的研究进展

面对日益严峻的能源紧缺与环境污染形势,电活性微生物(electroactive microorganisms)的电催化过程为实现绿色生产提供了新的思路。奥奈达希瓦氏菌具有独特的呼吸方式和电子传递能力,在微生物燃料电池、增值化学品的生物电合成、金属废物处理和环境修复系统等领域有着广泛的应用。奥奈达希瓦氏菌(Shewanella oneidensis MR-1)电活性生物被膜是实现电活性微生物电子传递过程的优良载体,其形成过程十分复杂且受到多种因素的影响和调控,在增强细菌环境抗逆性、提高电子传递效率等多方面发挥着十分重要的作用。本文较为系统地综述了奥奈达希瓦氏菌生物被膜的形成过程、影响因素及其在生物能源、生物修复和生物传感中的相关应用,为进一步实现其在更多领域的应用提供了理论基础。     

Electricity generation from glucose by a Klebsiella sp. in microbial fuel cells

As electrochemically active bacteria play an important role in microbial fuel cells (MFCs), it is necessary to get a comprehensive understanding of their electrogenesis mechanisms. In this study, a new electrochemically active bacterium, Klebsiella sp. ME17, was employed into an “H” typed MFC for electrogenesis, with glucose as the electron donor. The maximum power density was 1,209 mW/m² at a resistance of 340 Ω and the maximum current was 1.47 mA. Given the original anode medium, fresh medium, and the supernatant of the anode medium in the same MFC, respectively, the polarization curves illustrated that the strain produced mediators to promote extracellular electron transfer. The anode medium supernatant was electrochemically active, based on cyclic voltammogram, and the supernatant was very likely to contain quinone-like substances, as indicated by spectrophotometric and excitation–emission matrix fluorescence spectroscopy analysis. Further investigation on the color and ultraviolet absorbance at 254 nm of the filtered anode medium showed that the redox states of mediators strongly associated with the electricity generation states in MFCs.     

Long-term performance of a plant microbial fuel cell with Spartina anglica

The plant microbial fuel cell is a sustainable and renewable way of electricity production. The plant is integrated in the anode of the microbial fuel cell which consists of a bed of graphite granules. In the anode, organic compounds deposited by plant roots are oxidized by electrochemically active bacteria. In this research, salt marsh species Spartina anglica generated current for up to 119 days in a plant microbial fuel cell. Maximum power production was 100 mW m⁻² geometric anode area, highest reported power output for a plant microbial fuel cell. Cathode overpotential was the main potential loss in the period of oxygen reduction due to slow oxygen reduction kinetics at the cathode. Ferricyanide reduction improved the kinetics at the cathode and increased current generation with a maximum of 254%. In the period of ferricyanide reduction, the main potential loss was transport loss. This research shows potential application of microbial fuel cell technology in salt marshes for bio-energy production with the plant microbial fuel cell.     

Influence of anodic biofilm growth on bioelectricity production in single chambered mediatorless microbial fuel cell using mixed anaerobic consortia

The effect of anodic biofilm growth and extent of its coverage on the anodic surface of a single chambered mediatorless microbial fuel cell (MFC) was evaluated for bioelectricity generation using designed synthetic wastewater (DSW) and chemical wastewater (CW) as substrates and anaerobic mixed consortia as biocatalyst. Three MFCs (plain graphite electrodes, air cathode, Nafion membrane) were operated separately with variable biofilm coverage [control; anode surface coverage (ASC), 0%], partially developed biofilm [PDB; ASC approximately 44%; 90 days] and fully developed biofilm [FDB; ASC approximately 96%; 180 days] under acidophilic conditions (pH 6) at room temperature. The study depicted the effectiveness of anodic biofilm formation in enhancing the extracellular electron transfer in the absence of mediators. Higher specific power production [29mW/kg COD(R) (CW and DSW)], specific energy yield [100.46J/kg VSS (CW)], specific power yield [0.245W/kg VSS (DSW); 0.282W/kg VSS (CW)] and substrate removal efficiency of 66.07% (substrate degradation rate, 0.903kgCOD/m(3)-day) along with effective functioning fuel cell at relatively higher resistance [4.5kOmega (DSW); 14.9kOmega (CW)] correspond to sustainable power [0.008mW (DSW); 0.021mW (CW)] and effective electron discharge (at higher resistance) and recovery (Coulomb efficiency; 27.03%) were observed especially with FDB operation. Cyclic voltammetry analysis documented six-fold increment in energy output from control (1.812mJ) to PDB (10.666mJ) operations and about eight-fold increment in energy from PDB to FDB (86.856mJ). Biofilm configured MFC was shown to have the potential to selectively support the growth of electrogenic bacteria with robust characteristics, capable of generating higher power yields along with substrate degradation especially operated with characteristically complex wastewaters as substrates.